Benefit Plans (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended																		12 Months Ended									12 Months Ended																	12 Months Ended							12 Months Ended			12 Months Ended					12 Months Ended								12 Months Ended				12 Months Ended					12 Months Ended					12 Months Ended													12 Months Ended		12 Months Ended
	Dec. 31, 2012 Pension benefits	Dec. 31, 2011 Pension benefits	Dec. 31, 2010 Pension benefits	Dec. 31, 2012 Pension benefits Quoted prices in active markets for identical assets (Level 1)	Dec. 31, 2011 Pension benefits Quoted prices in active markets for identical assets (Level 1)	Dec. 31, 2012 Pension benefits Significant other observable inputs (Level 2)	Dec. 31, 2011 Pension benefits Significant other observable inputs (Level 2)	Dec. 31, 2012 Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2011 Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2010 Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2012 Postretirement benefits	Dec. 31, 2011 Postretirement benefits	Dec. 31, 2012 U.S. equity securities Pension benefits	Dec. 31, 2011 U.S. equity securities Pension benefits	Dec. 31, 2012 U.S. equity securities Pension benefits Quoted prices in active markets for identical assets (Level 1)	Dec. 31, 2011 U.S. equity securities Pension benefits Quoted prices in active markets for identical assets (Level 1)	Dec. 31, 2012 U.S. equity securities Pension benefits Significant other observable inputs (Level 2)	Dec. 31, 2011 U.S. equity securities Pension benefits Significant other observable inputs (Level 2)	Dec. 31, 2012 U.S. equity securities Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2011 U.S. equity securities Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2010 U.S. equity securities Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2012 International equity securities Pension benefits	Dec. 31, 2011 International equity securities Pension benefits	Dec. 31, 2012 International equity securities Pension benefits Quoted prices in active markets for identical assets (Level 1)	Dec. 31, 2011 International equity securities Pension benefits Quoted prices in active markets for identical assets (Level 1)	Dec. 31, 2012 International equity securities Pension benefits Significant other observable inputs (Level 2)	Dec. 31, 2011 International equity securities Pension benefits Significant other observable inputs (Level 2)	Dec. 31, 2012 International equity securities Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2011 International equity securities Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2010 International equity securities Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2012 Fixed income securities Pension benefits	Dec. 31, 2011 Fixed income securities Pension benefits	Dec. 31, 2012 U.S. government and agencies Pension benefits	Dec. 31, 2011 U.S. government and agencies Pension benefits	Dec. 31, 2012 U.S. government and agencies Pension benefits Quoted prices in active markets for identical assets (Level 1)	Dec. 31, 2011 U.S. government and agencies Pension benefits Quoted prices in active markets for identical assets (Level 1)	Dec. 31, 2012 U.S. government and agencies Pension benefits Significant other observable inputs (Level 2)	Dec. 31, 2011 U.S. government and agencies Pension benefits Significant other observable inputs (Level 2)	Dec. 31, 2012 Foreign government Pension benefits	Dec. 31, 2011 Foreign government Pension benefits	Dec. 31, 2012 Foreign government Pension benefits Significant other observable inputs (Level 2)	Dec. 31, 2011 Foreign government Pension benefits Significant other observable inputs (Level 2)	Dec. 31, 2012 Municipal Pension benefits	Dec. 31, 2011 Municipal Pension benefits	Dec. 31, 2012 Municipal Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2011 Municipal Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2010 Municipal Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2012 Corporate Pension benefits	Dec. 31, 2011 Corporate Pension benefits	Dec. 31, 2012 Corporate Pension benefits Significant other observable inputs (Level 2)	Dec. 31, 2011 Corporate Pension benefits Significant other observable inputs (Level 2)	Dec. 31, 2012 Corporate Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2011 Corporate Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2009 Corporate Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2010 Asset-backed securities ("ABS") Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2012 Residential mortgage-backed securities ("RMBS") Pension benefits	Dec. 31, 2011 Residential mortgage-backed securities ("RMBS") Pension benefits	Dec. 31, 2012 Residential mortgage-backed securities ("RMBS") Pension benefits Significant other observable inputs (Level 2)	Dec. 31, 2011 Residential mortgage-backed securities ("RMBS") Pension benefits Significant other observable inputs (Level 2)	Dec. 31, 2011 Residential mortgage-backed securities ("RMBS") Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2010 Residential mortgage-backed securities ("RMBS") Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2012 Short-term investments Pension benefits	Dec. 31, 2011 Short-term investments Pension benefits	Dec. 31, 2012 Short-term investments Pension benefits Quoted prices in active markets for identical assets (Level 1)	Dec. 31, 2011 Short-term investments Pension benefits Quoted prices in active markets for identical assets (Level 1)	Dec. 31, 2012 Short-term investments Pension benefits Significant other observable inputs (Level 2)	Dec. 31, 2011 Short-term investments Pension benefits Significant other observable inputs (Level 2)	Dec. 31, 2012 Short-term investments and other Pension benefits	Dec. 31, 2011 Short-term investments and other Pension benefits	Dec. 31, 2012 Real estate funds Pension benefits	Dec. 31, 2011 Real estate funds Pension benefits	Dec. 31, 2012 Real estate funds Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2011 Real estate funds Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2010 Real estate funds Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2012 Private equity funds Pension benefits	Dec. 31, 2011 Private equity funds Pension benefits	Dec. 31, 2012 Private equity funds Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2011 Private equity funds Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2010 Private equity funds Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2012 Hedge funds Pension benefits	Dec. 31, 2011 Hedge funds Pension benefits	Dec. 31, 2012 Hedge funds Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2011 Hedge funds Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2010 Hedge funds Pension benefits Significant unobservable inputs (Level 3)	Dec. 31, 2012 Cash and Cash Equivalents Pension benefits	Dec. 31, 2011 Cash and Cash Equivalents Pension benefits	Dec. 31, 2012 Cash and Cash Equivalents Pension benefits Quoted prices in active markets for identical assets (Level 1)	Dec. 31, 2011 Cash and Cash Equivalents Pension benefits Quoted prices in active markets for identical assets (Level 1)	Dec. 31, 2011 Free Standing Derivative Assets Pension benefits	Dec. 31, 2011 Free Standing Derivative Assets Pension benefits Quoted prices in active markets for identical assets (Level 1)	Dec. 31, 2011 Free Standing Derivative Assets Pension benefits Significant other observable inputs (Level 2)	Dec. 31, 2011 Free Standing Derivatives Liabilities Pension benefits	Dec. 31, 2011 Free Standing Derivatives Liabilities Pension benefits Quoted prices in active markets for identical assets (Level 1)	Dec. 31, 2011 Free Standing Derivatives Liabilities Pension benefits Significant other observable inputs (Level 2)	Dec. 31, 2012 Limited partnership interests Pension benefits	Dec. 31, 2011 Limited partnership interests Pension benefits	Dec. 31, 2012 Equity securities Pension benefits	Dec. 31, 2011 Equity securities Pension benefits
Pension plans' target percentage of plan assets and the actual percentage of plan assets
Target asset allocation, minimum range (as a percent)																															35.00%																																					1.00%																											12.00%		42.00%
Target asset allocation, maximum range (as a percent)																															48.00%																																					3.00%																											23.00%		55.00%
Actual percentage of plan assets	100.00%	100.00%																													38.00%	38.00%																																				3.00%	4.00%																										9.00%	10.00%	50.00%	48.00%
Notional amount of derivatives, maximum percentage of plan assets	115.00%
Cash collateral from target asset allocation, investment allocation (as a percent)																															28.00%																															72.00%
Total plan assets at fair value	$ 5,830	$ 5,178		$ 1,021	$ 811	$ 3,863	$ 3,429	$ 946	$ 938				$ 2,123	$ 892	$ 13	$ 11	$ 2,042	$ 817	$ 68	$ 64		$ 580	$ 1,347	$ 136	$ 116	$ 198	$ 986	$ 246	$ 245				$ 877	$ 754	$ 799	$ 634	$ 78	$ 120	$ 32	$ 26	$ 32	$ 26	$ 129	$ 163	$ 129	$ 163		$ 1,004	$ 878	$ 994	$ 869	$ 10	$ 9			$ 95	$ 119	$ 95	$ 119			$ 480	$ 527	$ 56	$ 33	$ 424	$ 494			$ 214	$ 192	$ 214	$ 192		$ 199	$ 186	$ 199	$ 186		$ 80	$ 79	$ 80	$ 79		$ 17	$ 18	$ 17	$ 18	$ 3	$ 1	$ 2	$ (6)	$ (2)	$ (4)
Total plan assets at fair value, allocation (as a percent)	100.00%	100.00%		17.50%	15.70%	66.30%	66.20%	16.20%	18.10%
Securities lending obligation	(463)	(554)
Other net plan assets	31	51
Total reported plan assets	5,398	4,675	4,669					946	938	992									68	64	6							246	245	253															129	163	222					10	9	10							48											214	192	167			199	186	166			80	79	120
Pension plan assets
Fair value of plan assets, beginning of year	4,675	4,669						938	992	1,103									64	6	4							245	253	233															163	222	344					9	10	10	32					48	61											192	167	135			186	166	149			79	120	135
Actual return on plan assets: Relating to assets sold during the period								30	36	(73)																				1															5							1	1		(1)					(8)	(10)											16	(1)	(4)			8	1					43	(59)
Actual return on plan assets: Relating to assets still held at the reporting date								3	10	118									7	(2)	2							1	(5)	7															(2)	1	(2)													8	23											2	29	3			(6)	22	19			1	(43)	66
Purchases, sales and settlements, net								(25)	(82)	(150)									(3)	60									(3)	12															(37)	(60)	(114)						(2)		(31)					(30)	(26)											4	(3)	33			11	(3)	(2)				(41)	(22)
Net transfers in and/or (out) of Level 3									(18)	(6)																																					(6)													(18)
Fair value of plan assets, end of year	5,398	4,675	4,669					946	938	992									68	64	6							246	245	253															129	163	222					10	9	10							48											214	192	167			199	186	166			80	79	120
Expected long-term rate of return on plan assets (as a percent)	8.50%	8.50%	8.50%
Expected long-term rate of return on plan assets for the next fiscal year (as a percent)	7.75%
Arithmetic average of the annual actual return on plan assets for the last 10 years (as a percent)	8.70%
Arithmetic average of the annual actual return on plan assets for the last 5 years (as a percent)	3.60%
Cash flows
Defined benefit pension plans, estimated employer contributions in next fiscal year	578
Employer contribution	439	264									39	41
Participant contributions	1	1									20	20
Estimated future benefit payments
2013	318										44
2014	345										45
2015	357										47
2016	383										48
2017	417										50
2018-2022	2,483										275
Total benefit payments	$ 4,303										$ 509